Reliable immunodiagnosis of B. Burgdorferi infection is crucial for the timely diagnosis of Lyme disease. Early treatment of Lyme disease is important to limit or prevent serious damage to the nervous and musculoskeletal system. Current serologic assays use cultured B. burgdorferi as their antigen source. Because OspA is the major protein expressed in cultured organisms, with the advent of OspA vaccines, all current whole B. burgdorferi ELISA's will become obsolete. Although these vaccines are efficacious, there are vaccine failures and the duration of protection against B. Burgdorferi infection is limited. In this project we will reformulate the array of epitopes in our diagnostic recombinant antigens to avoid cross-reactivity with the vaccine antigen (a recombinant OspA). This will allow sensitive, specific diagnosis of B. Burgdorferi infection regardless of vaccination status. In preliminary studies we have already shown that an assay based on chimeric recombinant proteins devoid of OspA epitopes is nearly as good as our assay using chimers containing OspA epitopes. In this Phase I project we will further refine the balance of epitopes, adding some to give improved sensitivity or improved coverage of genetic diversity, and eliminating others that limit specificity. This will set the stage for validation of the new recombinant-based immunoassays in Phase II. PROPOSED COMMERCIAL APPLICATIONS: In the US and Europe, about 5 million Lyme tests are performed each year. When OspA-based Lyme vaccines come on the market, essentially the entire diagnostic market will be open to the first company with an approved assay that can detect B. burgdorferi infection regardless of vaccination status.